More than 100,000 patients received percutaneous transluminal coronary angioplasty (PTCA in 1985; more than 160,000 procedures are expected to be performed in 1986. Technical improvements in the procedure now enable cardiologists to treat patients with more extensive coronary disease. Data from the 1985-86 NHLBI PTCA Registry confirm that current patients have more extensive disease, more lesions dilated, more cardiovascular risk factors, yet better immediate results than the patients with less severe disease who received PTCA between 1977 and 1982. With a therapy being applied to such a large segment of the population, it is imperative to evaluate objectively its short-and long-term risks and benefits. To do this, we propose to follow the 1985-86 cohort of 2,000 patients for 5 years. Experienced clinical coordinators at 16 Registry sites will contact each patient yearly to establish clinically apparent recurrence, mortality, morbidity, symptoms, additional revascularizations (including angiographic results), and functional status. We expect to maintain our track record of over 96% follow-up. To strengthen the validity of inferences to be derived from the 1985-86 registry, we will introduce a number of quality control measures, including central, computerized evaluation of all pre-and post-PTCA angiograms, training sessions, site visits, quality control on a random sample of clinical data, and exchange of a 10% sample of pre-PTCA films among centers. Event rates obtained from this study will provide a realistic basis for the design of the NHLBI Bypass Angioplasty Revascularization Investigation (BARI) that will begin recruitment in 1988. We have been the Data Coordinating Center for the NHLBI Registry since 1980 and are currently conducting a follow-up of the 1977- 1982 cohort. The well established collaborative arrangements with each of the participating clinical investigators assure that the high level of productivity will continue to yield clinically relevant and scientifically valid new information.